The invention relates to control apparatus of the type using a row (sometimes called a "gallery") of slots in a cylinder and slider arrangement for opening, closing, and regulating currents of gas, air, cold blast and flue gas for the air blast preheaters, also known as hot air stoves or cowpers of blast furnaces.
The hot air stove or air blast preheater supplies compressed and heated air (so called hot blast) to the blast furnace for the combustion of the heating material and for the conversion and activation of the reducing agents in the blast furnace. Regulating controls are provided in the hot blast line to regulate the amount and temperature of the hot blast and to keep such amounts and temperatures constantly at predetermined values, prior to introduction into the blast furnace, in order to keep the blast furnace operation as even and quite as possible. The blast preheaters are alternately heated up by combustion of gas, and supplied with cold blast to be converted by the preheaters into the hot blast for the blast furnace. Prior to the changeover for cold blast entering into the preheater, the preheater is filled up with air, up to a predetermined target pressure, in order to avoid any pressure drop in the cold blast duct and preheater, and accordingly in the hot blast duct from the blasting preheater, which would endanger the blast furnace operation. On the other hand, prior to the changeover from cold blasting to heating up of the preheater, air must be discharged from the preheater as the heating up is conducted at a pressure but slightly above the pressure of the atmosphere. Of course, this filling up and discharging of the preheater is to be performed as rapidly as possible, but it is also important not to disturb the supply of hot blast to the blast furnace, not to generate too much noise incident to the discharging of air from the preheater, and at the same time to keep the cost of the entire system within reasonable limits. For these purposes and others, also to maintain proper safety, large and complex control systems have been used for the preheaters, and the different parts of such control systems have been constructed in different form and dimensions, each depending on its particular function (for example, opening and closing as distinguished from regulating) and also depending on the aerostatic and aerodynamic conditions imposed on each control element. Different control elements were typically formed as slot-type valves or in other forms. As pressures, temperature and amounts of air or gas to be handled were constantly increased in blast furnace operation, the coast of the control elements and control systems tended to increase constantly. A series of control elements was needed in each of the several lines, connected to a blast preheater for performing different functions such as opening and closing the lines and regulating the filling up and discharge operations. In view of the high pressures, temperatures and quantities of flow, none of he controls as constructed and arranged up to now was suitable for performing several of these functions.
One of the control elements known to the art has used an open ended, slotted cylinder with a slider slidable therein by suitable power for fully closing, fully opening, or partly closing and partly opening the slots. Such controls were built with a housing around the cylinder and with first and second connectors, the first connector communicating with the space around the cylinder in the area of the slots and the other connector communicating with one or both of the open ends of the cylinder. Such a control element operates under balanced pressures, as the pressure of the fluid medium controlled thereby is uniformly applied to all sides of the slider and therefore does not influence the forces required for moving the slider. In addition, this type of control is not easily disturbed by changes of temperature of the fluid medium, and by resulting changes of expansion or contraction of the cylinder and slider. However, the control elements of this type, as known up to now, could be utilized only within narrow limits regarding their application to the various types and amounts of flows. For example, it was impossible to simply enlarge the total slot apertures provided by the devices built up to now, to accommodate larger amounts of flow. Even for reasons of strength of material such simple enlargement was impractical.